Thu, 30 Apr 2026 14:08:14 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3413&Focus=69372#Comment_69372 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3413&Focus=69372#Comment_69372 Thu, 17 Dec 2009 09:09:10 +0000 ChrisEngland
Chris]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3413&Focus=69373#Comment_69373 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3413&Focus=69373#Comment_69373 Thu, 17 Dec 2009 09:17:52 +0000 joe90
I would imagine that straw in compression had good decrement delay and its insulation value is also high but leaving asside the internal walls and floor does straw/clay/lime constitute high thermal mass?

Joe]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3413&Focus=69380#Comment_69380 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3413&Focus=69380#Comment_69380 Thu, 17 Dec 2009 10:10:12 +0000 Gotanewlife https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3413&Focus=69382#Comment_69382 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3413&Focus=69382#Comment_69382 Thu, 17 Dec 2009 10:38:57 +0000 fostertom Posted By: ChrisEnglandby adjusting the phasing of the passage of exterior warmth/coolth into the interiorThat's only the classic, well-known illustrative use of decrement , suitable for Arizona (blistering hot days, v cold nights). Other uses aren't so at-a-glance simple to understand, but believe me, decrement is happening all the time in every building, whether you build it into your calcs or not. I don't fully understand decrement yet but when I do, am sure it's an understanding that can be wonderously exploited in e.g. any kind of heat storage (whether in the structural elements, or remote). Understanding of decrement can also avoid unexpected and unwelcome temp swings even in simple state-of-art Passivhaus-type interiors, where the sun comes in thro windows and is expected to be soaked up (preventing overheating), stored and released by the heavy surfaces the radiation falls on.

Anyone know of any plain-language texts that explain decrement (not just its promised effect, but how it works) without resorting to equations and calculus?]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3413&Focus=69394#Comment_69394 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3413&Focus=69394#Comment_69394 Thu, 17 Dec 2009 11:36:20 +0000 ChrisEngland While decrement may have some role to play, I'm concerned that what you're actually talking about are the detailed thermal flows, which are going to be so variable that little can be extracted from them, other than in highly specific locations - e.g. your Arizona example - except the more general concept of thermal mass - on which point, and regarding your Passivhaus comment, I've always thought thermal mass would be better inside the house (as opposed to the external walls) with both high mass and high conductivity - something like thick concrete (hiss) internal walls interlaced with steel to get the warmth in and out. I'd be glad to be proved wrong, however.

Gotanewlife - I can't really state an optimum mass, but that soundes reasonable - obviously what you'd need would vary with location/air-tightness and of cource cost would come into it. As above, I believe internal mas swould be better than perimeter.

Chris]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3413&Focus=69402#Comment_69402 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3413&Focus=69402#Comment_69402 Thu, 17 Dec 2009 12:39:56 +0000 djh
Water has high thermal mass and can move large quantities of heat around (by convective or pumped motion rather than by conductivity). It can be a pretty good alternative to concrete if you want added thermal mass.

Tom, I'm not sure what kind of explanation you're looking for. Heat is vibration of atoms. Heat moves by these vibrations being passed on from one atom to another. The passing on takes time, depending on what atoms are involved and how they're connected together (think of a Newton's cradle toy, for example) and there's a constant averaging, smearing of temperature differences goes on because the vibrations spread in all directions from everywhere. So there's a delay and the variation is decremented.

Cheers, Dave

PS As an aside, the term 'decrement delay' is two words and they both have a point. The delay obviously refers to the time it takes heat to pass through walls etc. The decrement refers to the fact that the amplitude of external temperature oscillations is reduced inside the building. So I think decrement delay is quite a good name for the phenomena.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3413&Focus=69419#Comment_69419 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3413&Focus=69419#Comment_69419 Thu, 17 Dec 2009 14:20:40 +0000 fostertom Posted By: djhI've read elsewhere that the time constant in typical passivhaus-type interiors tends to be several daysI'd love to see that, Dave.

I'd thought only 1.5 days, 2 days max, which explain why Passivhaus still requires back-up heating, and always will even if insulation etc increased even more. 1.5 to 2 days is v far short of what's reqd to bridge over typical sunless spells.

I'm working on increasing that to say 10 days, still within the above-ground structure (NB this is a different line of enquiry than underground/interseasonal storage, tho there's much cross-over). That in turn means that far more heat has to be collected and put into storage. Capturing more of what's available, when the sun shines, increases risk of overheating. So it's about ways and means, then a different set of prudent balances between collection/loss/overheating etc, compared to Passivhaus's set of prudent balances.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3413&Focus=69422#Comment_69422 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3413&Focus=69422#Comment_69422 Thu, 17 Dec 2009 14:26:04 +0000 fostertom Posted By: djhthe term 'decrement delay' is two words and they both have a point. The delay obviously refers to the time it takes heat to pass through walls etc. The decrement refers to the fact that the amplitude of external temperature oscillations is reduced inside the building. So I think decrement delay is quite a good name for the phenomenaI agree - will do, from now on.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3413&Focus=69444#Comment_69444 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3413&Focus=69444#Comment_69444 Thu, 17 Dec 2009 18:06:15 +0000 djh Posted By: fostertomI'd love to see that, Dave.
I read it on the AECB forum, IIRC, Tom.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3413&Focus=69588#Comment_69588 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3413&Focus=69588#Comment_69588 Sun, 20 Dec 2009 00:55:27 +0000 mike7
Apart from that, the 3.6 figure is the difference between the two formulae. That's probably due to a combination of using seconds in one place versus hours in the other and a factor of 1000 somewhere in the units. Brain fade took over at this point.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3413&Focus=69636#Comment_69636 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3413&Focus=69636#Comment_69636 Sun, 20 Dec 2009 22:26:41 +0000 sinnerboy https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3413&Focus=69920#Comment_69920 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3413&Focus=69920#Comment_69920 Tue, 22 Dec 2009 20:04:38 +0000 sinnerboy
"Draws a detail of wall or roof sections, calculates U-value, Time Lag, and Decrement Factor. It plots temperature drop through the section. Draws 2-D daily and 3-D annual plots of Outdoor and Sol-Air Temperatures, Normal and Total Surface Radiation, and Heat Flow through the envelope. It was originally called SOLAR-3. Unzip the download and install OPAQUE by clicking on SETUP.EXE, and to see the Users Manual open Manual.txt"

http://www.energy-design-tools.aud.ucla.edu/tools/opaque2-1.zip

here

http://www.energy-design-tools.aud.ucla.edu/]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3413&Focus=70156#Comment_70156 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3413&Focus=70156#Comment_70156 Sun, 27 Dec 2009 00:51:25 +0000 mike7
"1st one
Thermal lag = 1.382*thickness * sqr(density*specific heat / 3.6*thermal conductivity)

2nd one
tl = 1.38 * L * SQRT(1/a)

where:
tl = time lag (in hours)
L = Thickness of component (unit?)
a = thermal diffusivity, = thermal conductivity / (density * specific heat)"


The dimensions don't work out, never mind the units. The formula has to be something like this:

tl hrs = L squared x sp.ht x density / (conductivity x C)

where C is a constant somewhere in the region of 20,000, L is in metres, sp.ht is in J/kg.degK, density is in kg/m^3, and conductivity is in W/m.degK]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3413&Focus=70377#Comment_70377 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3413&Focus=70377#Comment_70377 Wed, 30 Dec 2009 11:18:08 +0000 mike7
(Re the formulae first quoted - I wonder if there wasn't just a mis-transcription somewhere along the way, squareroot instead of squared. That would account for the difference)]]>